I will try and answer your question with some experiences I have had.
As with most agents, I normally do not take clients that are not pre-qualified.
These two clients somewhat begged and pleaded and promised to work on their pre-qual soon and I took them on as clients mainly because they were friends.
The first client we looked at an area for $400K-$500K homes as she told me this was her budget. After about 6 outings she finally got her pre-qualified and it was for $700K. She was surprised at the higher amount and totally lost interest in the area we had been searching in and started looking elsewhere. A positive ending except for the fact we wasted 6 days in the wrong area and price.
The second client I showed her around about 6 times as well and for her budget price of @ $300K. On that 6th time, she found her dream house and finally then did she apply for a pre-qual. I called and called her the next few weeks inquiring as to how the pre-qual was going. I didn't get a hold of her for two months. After I did get a hold of her she mentioned she was told she had real bad credit, was denied, and it would take her over a year to fix her credit report. A negative spin and 6 days of our time wasted.
A pre-qual informs you as well as the agent what your real budget is so you don't waste your time as well as his. Showing clients properties take about 4 hours each outing. If you go out with an agent just 6 times that's about 24 hours that is wasted if you end up not qualifying or qualify for a different amount than what you were looking for. Getting a pre-qual also lets people know you are serious about buying a home.
Let me ask you a question. I understand you are not ready to buy until December but there is no penalty in getting a pre-qual early so why are you not trying to get pre-qualified?